Ensure VarRef inherits dtype when varp is set.

Inlining used to set some VarRefs to point to new Var nodes, without
updating the dtype of the VarRef to the dtype of the new Var.
AstNode::sameTree does identity comparison on the dtype, so some trees
that were semantically the same did not compare as such with sameTree
because of the dtype. This in turn results in some missed opportunities
for combining equivalent SenTree sensitivities when the clock came from
outside.

src/V3Inst.cpp

@@ -443,7 +443,6 @@ private:
                 string newname = varrefp->name() + "__BRA__" + cvtToStr(i + offset) + "__KET__";
                 AstVarXRef* newVarXRefp = new AstVarXRef(nodep->fileline(), newname, "", true);
                 newVarXRefp->varp(newp->modVarp());
-                newVarXRefp->dtypep(newp->modVarp()->dtypep());
                 newp->exprp()->unlinkFrBack()->deleteTree();
                 newp->exprp(newVarXRefp);
                 if (!prevPinp) {